Glucagon, a hormone secreted by the pancreas, is a polypeptide consisting of a single chain of 29 amino acids with a molecular weight of 3,485 Da. Glucagon stimulates the liver to convert stored glycogen into glucose, which is released into the blood. Medically, glucagon is used primarily to treat hypoglycemia (a condition of lower than normal blood glucose concentrations) due to insulin overdose. Glucagon is also used during radiologic examinations of the stomach, duodenum, small bowel, and colon when diminished intestinal motility is required. For pharmaceutical use, glucagon can be made by chemical synthesis, recombinant DNA technology or derived from an animal source.
The two currently marketed glucagon drug products, GlucaGen® Hypokit (glucagon hydrochloride) from Novo Nordisk A/S and Glucagon for Injection (rDNA Origin) from Eli Lilly and Company (“Glucagon Emergency Kit for Low Blood Sugar”) are provided as two-part kits. The GlucaGen® Hypokit consists of a vial containing 1 mg glucagon as hydrochloride and 107 mg lactose monohydrate in a lyophilized solid (“lyo cake”) and a disposable syringe that contains sterile water for reconstituting the lyo cake. The lyo cake provides a dry environment that keeps glucagon chemically stable. The reconstituted solution contains glucagon as hydrochloride 1 mg/mL (1 unit/mL) and lactose monohydrate (107 mg) at pH 2.5-3.5. The Glucagon Emergency Kit for Low Blood Sugar contains a vial of sterile lyophilized glucagon and a syringe of sterile diluent. The lyo cake contains 1 mg (1 unit) of glucagon and 49 mg of lactose. The diluent syringe contains 12 mg/mL of glycerin, Water For Injection, and hydrochloric acid. The reconstituted solution contains glucagon 1 mg/mL (1 unit/mL) glucagon and 49 mg/mL lactose at pH 2.0-3.5. To use the Kit, the diluent is first injected into vial with the lyo cake to dissolve it. The reconstituted glucagon solution obtained is then drawn back into a syringe and then injected. The reconstituted glucagon solutions for both the GlucaGen® Hypokit and the Glucagon Emergency Kit for Low Blood Sugar thus obtained are chemically and physically unstable and therefore must be used immediately. The glucagon used in both kits is produced by DNA recombinant technology.
Insulin pumps have been widely used by type-1 diabetics for over a decade. An insulin pump can be worn by a patient externally in close proximity to the body and delivers insulin via fine tubing through subcutaneously implanted needles. The subcutaneous needles may remain in place for up to a week. Continuous glucose monitoring sensors or “CGM” capable of continuously reading blood glucose levels can be used to provide blood glucose level information to the insulin pump to control insulin output in real time. However, when too much insulin has been pump-delivered, the current versions of the insulin pump do not have an effective means to counteract the drop in blood glucose and impending hypoglycemia from the already-administered insulin. In the normal individual, the pancreas naturally counteracts rapid blood glucose decreases by secreting glucagon, but in a Type-1 diabetic patient, such function is impaired due to the diminished alpha cell activity.
A “bi-hormonal artificial pancreas” consisting of a CGM-controlled bi-hormonal pump that delivers both insulin and glucagon, has the potential to closely control blood glucose levels. When blood glucose reaches or is anticipated to reach hypoglycemic levels, the bi-hormonal pump could deliver glucagon to counteract instances of insulin-induced hypoglycemia. This dual drug capability will allow better blood glucose regulation similar to that achieved by the insulin/glucagon system of the normal pancreas.
A bi-hormonal pump requires a liquid glucagon formulation that is chemically and physically stable for at least 3.5 to 7 days at or near body temperature. Currently, insulin pump users replenish insulin approximately every half week. Therefore, 3.5-7 days was selected as a convenient replenishment cycle. Furthermore, the glucagon formulation must be “pump-able”, i.e., it can be delivered accurately and reliably in small volumes (e.g., 10-50 microliters) by a pump through narrow-bore infusion tubing. To be pump-able, the glucagon formulation must also have an acceptable viscosity and be chemically compatible with the pump and infusion set. For this reason, strong solvents such as DMSO are not desired.
Glucagon has an isoelectric point of 7.1 and is thus insoluble in water at physiological pH (pH 4-8). At pH 3 or lower, it is initially soluble, but within hours, it will aggregate to form a gel. The gelled glucagon consists predominantly of β-sheets or fibrils (Chou, P. Y., et al. 1975. Biochemistry 14(11):2536-2541) and can clog up the narrow tubing of the infusion set. Therefore, gelled or aggregated glucagon preparations are thus not pump-able. The glucagon fibrils or gels are also unsafe for injection.
In addition to forming gels, glucagon undergoes various types of chemical degradation. In solution, glucagon rapidly degrades chemically to form numerous degradation products. At least 16 degradation products of glucagon have been identified with the major degradation pathways being aspartic acid cleavage at positions 9, 15, and 21 and glutaminyl deamidation at positions 3, 20 and 24 (Kirsch, L. E., et al. 2000. International Journal of Pharmaceutics, 203:115-125). The chemical degradation of glucagon is rapid and complex. For example, a glucagon solution prepared from the GlucaGen® Hypokit loses about 60-70% of glucagon within 7 days at 37° C. (see Example 2). Therefore, the current commercial glucagon kits are not suitable for a bi-hormonal pump use.
Preventing glucagon degradation in aqueous solutions is very difficult and no effective method has been reported to effectively inhibit glucagon gelling and degradation.
WO 2013086292 A1 discloses glucagon formulations comprising glucagon, a bulking agent, and an acidifying agent in a pharmaceutically acceptable diluent. The composition can be readily lyophilized and rapidly reconstituted with its diluent. The bulking agents may include carbohydrates, amino acids, salts, mannitol, lactose, sucrose, dextran, sodium chloride, and combinations thereof. A bulking agent or matrix builder must provide a solid structure (i.e., a “cake”) or a powder after lyophilization. The disclosed formulation used mannitol as a bulking agent at concentrations from approximately 1.0% to approximately 10.0% (w/v).
WO2012059764 teaches aqueous compositions having a pH between 4 and 7 comprising glucagon and a cationic surfactant as solubilising agent. Examples of cationic surfactants include benzethonium salts, benzalkonium salts, and cetyl trimethylammonium salts. Cationic surfactants are toxic and not desirable for the long-term chronic use contemplated for the bi-hormonal pump.
WO 2011049713 claims a formulation comprising a sugar and a surfactant, wherein “sugar” refers to a monosaccharide or disaccharide with preferred examples including sucrose, maltose and glucose in a concentration range of about 20-100 mg/mL, preferably 0.25 M (which is equivalent to 8.6% w/v, 8.6% w/v and 4.5% w/v, respectively, for sucrose, maltose and glucose).
US20120232001 claims a stable formulation comprising: (a) a peptide or a salt thereof, wherein the peptide has been dried in a non-volatile buffer, and wherein the dried peptide has a pH memory that is about equal to the pH of the peptide in the non-volatile buffer; and (b) an aprotic polar solvent wherein the moisture content of the formulation is less than 5%, and wherein the dried peptide maintains the pH memory that is about equal to the pH of the peptide in the non-volatile buffer when the dried peptide is reconstituted in the aprotic polar solvent. Examples of aprotic polar solvents include dimethylsulfoxide (DMSO), dimethylformamide (DMF), ethyl acetate, n-methyl pyrrolidone (NMP), dimethylacetamide (DMA), and propylene carbonate. Formulations described therein are essentially non-aqueous. The safety of the aprotic polar solvents for the chronic use contemplated for the bi-hormonal pump is questionable.
WO1995032730 discloses a pharmaceutical preparation comprising glucagon and a stabilizing amount of a pharmaceutically acceptable ampholyte except histidine.
None of the above disclosed compositions can meet all of the following requirements desired for a new glucagon formulation:                1. Comprises an aqueous solution        2. Stable (i.e., non-gelling and chemically stable) for 3.5 to 7 days at 37° C.        3. Pump-able.        
There still is a need for pharmaceutical formulations of glucagon that overcome the limitations of the above described approaches.